Recent clinical trial and review put valuable evidence on the table 06/13/2019
Most givers of nutrition advice tell people it’s a good idea to eat a good breakfast.
That guidance makes good sense, because our brains need fuel to function and learn.
But the wisdom of that advice isn’t as clear when it comes to adults who are trying to lose weight.
So, researchers have been conducting clinical studies intended to determine which kinds of breakfasts — big, skimpy, or none — work better for weight control.
As we reported in Do Big Breakfasts Win for Weight Control?, some clinical studies suggest that big breakfasts aid efforts to shed and keep off unwanted pounds.
And the results of some studies suggest that — versus high-carb breakfasts — ones high in fat and/or protein are better for weight control: see Do Fatty Breakfasts Boost Fat-Burning?, High-Protein Breakfasts Help Blood Sugar Control, Protein for Breakfast Allays Appetites All Day, and Can Paleo-Style Breakfasts Curb Food Cravings?.
Of course, the kind of grain-based foods featured in a high-carb breakfast — whole-grain cereals or baked goods versus starchy products like bagels or white bread — really matters, given their widely differing effects on blood sugar.
The opposing outcomes of various clinical studies aren’t terribly surprising, because they’ve involved different kinds of people and employed different designs.
To help resolve those conflicting findings, Australian researchers reviewed the evidence from more than a dozen clinical trials — and their conclusions provide what may be the best guidance to date.
In brief, their analysis of previous clinical studies suggests that — versus eating a substantial breakfast — skipping breakfast aids weight control efforts.
Aussie’s evidence review challenges breakfast-weight assumptions
The new evidence review comes from a team at Melbourne, Australia’s Monash University.
They analyzed the evidence from 13 randomized, controlled clinical trials published over the past 28 years, mostly conducted in the U.S. and the UK, whose length ranged from 24 hours to four months (Sievert K et al. 2019).
Several of these trials focused on the effects on body weight of eating or skipping breakfast, while others examined the effect of eating breakfast on average daily calorie intakes.
Participants in the various trials included people who fell into various categories:
- Habitual breakfast eaters
- Habitual breakfast-skippers
- Breakfast eaters and breakfast skippers
- Leaner people, overweight people, or both
And the intriguing results of the evidence review hold significant practical implications — especially for folks who are trying to shed excess weight.
Their analysis revealed that — compared with people who didn’t eat breakfast — people who ate breakfast consumed an average of 260 more calories daily.
Further, the results of the Aussies’ analysis showed that on average, people who skipped breakfast were 0.44 kg (almost 1 lb.) lighter.
Somewhat surprisingly, the evidence review's authors concluded that the effect on weight of eating breakfast did not differ between people of normal weight versus those who were overweight.
The review authors noted that the quality and designs of the trials included in their review varied, so their own findings can’t be considered conclusive.
However, as they wrote, “… currently, the available evidence does not support modifying diets in adults to include the consumption of breakfast as a good strategy to lose weight ... [and] ... caution is needed when recommending breakfast for weight loss in adults, as it may have the opposite effect.”
Breakfast choices also depend on priorities and preferences
Skipping breakfast entirely deprives a foggy morning brain of fuel, so it's important to decide on your top priority: weight control versus optimal brain performance in the morning.
Of course, you could try eating a light, lower-carb breakfast, which would give your brain some fuel without spiking your blood sugar.
In an opinion essay concerning the Australian evidence review, professor Tim Spector of King’s College London, noted that people prefer to eat at different times, which, as he said, “might suit our unique personal metabolism” (Spector T 2019).
Spector also stressed the wide variations in people’s genetics and metabolisms, and the fact that official, slow-to-change diet guidelines often rest on outdated or erroneous information: “While waiting for guidelines to change, no harm can be done in trying out your own personal experiments in skipping breakfast”.
Why might skipping breakfast aid weight control?
Researchers have proposed two possible reasons why eating breakfast might aid weight loss:
- Consuming calories early in the day might dampen appetites and thereby reduce hunger and calorie intakes later in the day.
- Consuming calories early in the day might raise metabolic (calorie-burning) rates, and keep them higher than otherwise, thereby reducing hunger and calorie intakes later in the day and in the evening.
But the Australian team's evidence review found no significant difference in metabolic (calorie-burning) rates between breakfast-eaters and breakfast-skippers.
And, contrary to intuition and common belief, skipping breakfast was not linked to feeling hungrier in the afternoon — or to differences in metabolic rates or the resulting number of calories burned.
Lean people may benefit more from skipping breakfast
Two years ago, British researchers published the results of a clinical trial conducted in lean and obese people.
Their trial was designed to determine whether eating breakfast exerts different effects on the metabolisms and fat cells of lean versus obese people.
The research was led by Javier Gonzalez, Ph.D., at Britain's University of Bath. The trial involved 49 adults who were asked to either have breakfast or fast until noon, every day, for six weeks.
Based on their body mass index (BMI), 29 could be classified as lean, while 20 met the criteria for being considered obese.
The participants in the breakfast group consumed 350 calories within two hours of waking, while those in the fasting group consumed no calories until noon.
Before and after the clinical trial, the team examined the patients' markers of cardiometabolic health, their appetite responses, and their body fat distribution.
In addition, they monitored the activity of 44 genes that regulate key proteins involved in metabolism, and the ability of the participants’ fat cells to absorb glucose (blood sugar) when their bodies released insulin in response to consumption of food.
In lean people, skipping breakfast for six weeks activated genes that stimulate fat-burning, therefore raising their metabolic (calorie-burning) rates. However, this effect was not seen in the obese volunteers.
These findings revealed that the fat cells in the obese people could not take up as much glucose in response to insulin compared with the lean participants: an effect that appeared proportional to a person’s proportion of body fat (i.e., more body fat, less uptake of glucose).
This phenomenon explains why obese people are at greater risk for diabetes, a condition characterized by chronically high blood sugar levels.
Gonzalez and his team think that this may also be an attempt by the bodies of obese people to limit the amount of glucose their fat cells can take, to avoid storing additional fat.
As Gonzalez said, “By better understanding how fat responds to what and when we eat, we can more precisely target those mechanisms. We may be able to uncover new ways to prevent the negative consequences of having a large amount of body fat, even if we cannot get rid of it.”
He also noted some limitations of the study: “Since participants ate high-carb breakfasts, we cannot necessarily extrapolate our findings to other types of breakfasts, particularly those with high protein content.”
- Gonzalez JT, Richardson JD, Chowdhury EA, Koumanov F, Holman GD, Cooper S, Thompson D, Tsintzas K, Betts JA. Molecular adaptations of adipose tissue to 6 weeks of morning fasting vs. daily breakfast consumption in lean and obese adults. J Physiol. 2018 Feb 15;596(4):609-622. doi: 10.1113/JP275113. Epub 2017 Dec 20.
- Sievert K, Hussain SM, Page MJ, Wang Y, Hughes HJ, Malek M, Cicuttini FM. Effect of breakfast on weight and energy intake: systematic review and meta-analysis of randomised controlled trials. BMJ. 2019 Jan 30;364:l42. doi: 10.1136/bmj.l42.
- Spector T. Breakfast—the most important meal of the day? January 30, 2019. Accessed at https://blogs.bmj.com/bmj/2019/01/30/tim-spector-breakfast-the-most-important-meal-of-the-day/